Fetal tissues are comprised of many undifferentiated cells that proliferate actively, highly activated cells, nascent vascular endothelial cells, and so on. Although these are stringently regulated in fetal tissues and inhibited as individuals mature, this can be considered very similar to the state of a solid tumor except that the activity is regulated. Therefore, some of the genes expressed specifically in fetal tissues (fetal genes) can be genes involved in the phenomena characteristic of solid tumors such as abnormal growth, immortalization, infiltration, metastasis, and angiogenesis. In addition, some diseases other than cancers are also supposed to arise because fetal genes, which are repressed in a normal living body, are abnormally activated. Therefore, genes involved in various diseases such as cancers can be screened by isolating and analyzing fetal genes. Furthermore, development of medicines using novel action mechanisms is thought to be possible by designing drugs targeted on the genes.
Recently, as fetal genes which are assumed to be involved in malignant transformation, genes for surviving (Nat. Med., 3:917–921, 30 1997), aurora kinase (EMBO J., 17:3052–3065, 1998) and LYAR (Genes Dev., 7:735–748, 1993) have been reported. Their expressions are all activated in colon cancer, leukemia cells, and such, and these genes are thought to contribution importantly to the malignant transformation. In fact, it has been demonstrated that survivin has the apoptosis inhibitor activity, and aurora kinase participates in the cell cycle regulation as their physiological functions, indicating that acquiring function of either of them works favorably for cancer cells.